U.S. Pat. No. 5,198,170 teaches the manufacture of extruded profiles directly from powder or from preprocessed cubes. The obtention of smooth dull surface characteristics is found in the selection of small particle size and low friability PVC resin extruded in a relatively low extrusion stock temperature range as well as using a relatively higher extrusion stock temperature range with a compound containing a less friable resin. There is no teaching on the effects of using different twin screws on extrudate surface characteristics. The precise degree of work history required in the direct twin screw extrusion of profiles from powder PVC compound occurs within a narrow process window when one desires a surface texture which is smooth and dull. Where a higher extrusion output is wanted, the process window shifts, requiring modifications. According to U.S. Pat. No. 5,198,170 it is suggested that low shear extrusion screws be used. The acceptable surface characteristics of an extruded profile is a smooth but dull surface. A glossy surface is not desired. A smooth dull surface is obtained by achieving predominately primary particle flow in the melt. This means that fusion is not complete and particle flow still predominates. It is known that if too high fusion is obtained, the extruded profile becomes glossier, exhibits more orange peel, is more difficult to, and retain part dimension, and with too much stress this later can cause warpage in use. In the direct powder extrusion of compounds suggested in U.S. Pat. No. 5,198,170 wherein the PVC resin has a small particle size of up to 125 microns, it has been observed that these powder compounds have low bulk density. The low bulk density is a primary factor in limiting the output rate of extrusion. Therefore, powder compounds having high bulk density are desired where higher extrusion rates are needed.
Recently, efforts have been made to achieve higher extrusion output. Conical twin screws have just been introduced in the industry which create a higher rate of work level (high shear). It has been found that prior art powder formulations can be used to extrude acceptable looking profiles using these new screw designs, however the output rate must be substantially reduced in order to do this. It has thus been observed that PVC compounds suggested in the prior art do not work in the high output process window available with higher shear conical twin screws. As higher extrusion output rate is desirable, it would therefore be advantageous to provide a higher shear, high output twin screw extrusion process for making profiles other than pipe, especially vertical louver slats, having the desired surface aesthetics.